1. Field of the Invention
The present invention relates to an optical receiver, in particular, relates to an optical receiver for the avalanche photodiode.
2. Related Prior Art
Optical communication often uses an avalanche photodiode (hereinafter denoted as APD) for a light-receiving device because the an APD has an intrinsic characteristic to multiply photo carriers and to output a photocurrent relatively larger than that of a PIN photodiode. Japanese Patent Application published as 2004-040239 has disclosed a method for controlling the photocurrent generated in the APD by controlling a bias voltage applied to the APD.
On the other hand, it is necessary that, when the optical communication system equips a fiber amplifier, an excess optical input power, such as over 0 dBm, enters the APD due to an optical surge or an operational miss handling. Receiving such excess optical power at the optical receiver, the APD generates excess carriers, which is equivalent to the excess photocurrent, and may be broken itself by this photocurrent.